Dynamic monitoring of minimal residual disease in newly‐diagnosed multiple myeloma
Authors: Peiyu Yang, Weiling Xu, Xinyue Liang, Shanshan Yu, Xingcheng Yi, Mengmeng Liu, Mengru Tian, Tingting Yue, Yingjie Zhang, Yurong Yan, Zhongli Hu, Qiang Guo, Nan Zhang, Jingxuan Wang, Xiaoxiao Sun, Rui Hu, Shaji K. Kumar, Yun Dai, Fengyan Jin
Journal: American Journal of Hematology (2022)

With the introduction of novel agents, more than 80% of patients with newly-diagnosed MM (NDMM) can achieve complete remission (CR) or better after first-line treatment.1 However, the majority of these patients eventually experience relapse, therefore calling for an additional approach to more precisely evaluate the depth of response and estimate the outcomes. Minimal residual disease (MRD) has been emerging as a reliable surrogate endpoint for progression-free survival (PFS) in clinical trials, while undetectable MRD strongly correlates with favorable outcomes, including both PFS and overall survival (OS).2 Over 50 ongoing phase III trials have included MRD as an endpoint to evaluate the depth of therapeutic response or assign MRD-directed treatment. Thus, MRD has been included into the revised International Myeloma Working Group (IMWG) criteria for assessment of therapeutic response.3 Moreover, the prognostic value of MRD seems independent of baseline risk factors such as advanced disease stage (e.g., ISS or R-ISS III) and high-risk cytogenetic abnormality (HRCA).4 However, several key issues remain to be addressed for incorporating the MRD test into daily practice.5 To this end, we conducted this retrospective study to explore the significance of dynamic monitoring of the MRD status in the management of NDMM patients. This study was approved by the Institutional Review Board (IRB) of the First Hospital of Jilin University (approval # 2018-087). The study included patients with NDMM who had flow cytometry-based MRD test at least twice after initiation of treatment, between March 2015 and June 2019. CAs were assessed by FISH in CD138+ cells isolated from bone marrow (BM) samples via routine diagnostic procedures. Among them, del(17p), t(4;14), t(14;16), and + 1q (1q21 gain/amplification) were considered as HRCAs.3 Therapeutic responses were evaluated according to the IMWG consensus criteria.3 The first MRD test was conducted at the time when an objective response (e.g., PR, VGPR, CR, or sCR) was achieved during induction or consolidation. MRD was evaluated in bone marrow (BM) samples (1.5 × 107 cells per sample) using a modified 2-tube 8-color assay (tube 1: cKappa-FITC/cLambda-PE/CD138-Percp-cy5.5/CD27-PE-CY7/CD22-APC/CD19-APC-H7/CD38-BV421/CD45-Viogreen; tube 2: CD56-FITC/CD200-PE/CD28-Percp-cy5.5/CD117-PE-CY7/CD19-APC/CD20-APC-H7/CD38-BV421/CD45-Viogreen.) by Navios flow cytometer (Beckman Coulter) in a single clinical laboratory. Two million cellular events were analyzed using the Kaluza Analysis Software to determine the percentage of phenotypically aberrant clonal plasma cells (PCs) in total nucleated cells. The limit of detection (LOD) achieved was calculated in each sample according to the following formula: (20/number of viable nucleated cells) × 100.4 Undetectable MRD was defined as the absence of phenotypically aberrant clonal PCs or their percentage below the LOD (median 3.46 × 10−5), while detectable MRD was defined as the percentage of phenotypically aberrant clonal PCs equal to or greater than the LOD. Duration of undetectable MRD was defined as the time from the first detection of undetectable MRD to reappearance of detectable MRD. PFS was defined as the time from the first day of treatment until the date when disease progression, relapse, or death was first reported. OS was defined as the time from the first day of treatment until the date of death due to any cause or last follow-up. All statistical analyses were conducted using SPSS software (version 22.0) and R packages survival and survminer in R/Bioconductor (version 3.6.1). p < .05 was considered significant. A total of 220 patients with NDMM were assessed for MRD at least twice, with median of three times (range 2–11). The first test was conducted at initial objective responses, including PR (38.2%), very good partial response (VGPR, 19.1%), and ≥ CR (42.7%). Among them, 114 patients attained undetectable MRD (MRD−), while 106 patients had persistent MRD (MRD+). To examine whether baseline variables would influence the MRD status, clinical characteristics and treatment were compared between MRD− and MRD+ (Table S1). Interestingly, patients with ≥2 HRCAs (named double-hit) had lower rate of MRD− attainment (25.0%) than those with one HRCA (53.9%; p = .007). With the median follow-up time of 33.3 months, the Kaplan–Meier curve revealed that attainment of MRD− substantially prolonged PFS (Hazard ratio/HR, 0.19, 95% CI, 0.12–0.28, p < .0001; Figure S1A) and OS (HR, 0.25, 95% CI, 0.15–0.42, p < .0001; Figure S1B). Similar results were obtained in the subgroup of elderly patients (age ≥ 65 years), including PFS (p < .0001; Figure S1C) and OS (p = .0049; Figure S1D). Whereas the time-to-MRD− varied, virtually all MRD− patients achieved MRD− within a year (70% within half a year) after initiation of treatment (not shown). Accordingly, 1-year landmark analysis was conducted and revealed that MRD− were significantly associated with prolonged PFS (p < .001 for both time periods; not shown) and OS (Figure 1A) within or beyond 1 year. Three-year PFS rate of MRD− and MRD+ patients was 58.9% versus 12.4%; 5-year OS rate of MRD− and MRD+ patients was 67.5% versus 21.7%. Subgroup analysis according to the MRD status revealed that the favorable impact of MRD− on both PFS (Figure S1E) and OS (Figure S1F) was consistent across all subgroups categorized by various risk factors at diagnosis. Following the univariate analysis (Table S2), the multivariate Cox analysis adjusted for either individual risk factor (Table S3) or in combination (e.g., R-ISS III; Table S4) revealed that MRD− was the strongest predictive factor for PFS and OS. Altogether, these observations support that the MRD status is a powerful predictor for outcomes of NDMM patients, independent of virtually all risk factors at diagnosis. Analysis using the Cox proportional hazards model revealed no significant impact of all baseline characteristics on the duration of MRD− (Figure S2A; p > .05 for each case). The IMWG guideline defines sustained MRD-negative as MRD negativity confirmed a minimum of 1 year.3 MRD− duration ≥12 months markedly improved PFS (HR, 0.17, 95% CI, 0.09–0.34, p < .0001) and OS (HR, 0.31, 95% CI, 0.13–0.76, p = .0098). Similarly, MRD− duration ≥6 months also significantly prolonged PFS (HR, 0.16, 95% CI, 0.06–0.42, p = .0002) and OS (HR, 0.12, 95% CI, 0.03–0.47, p = .0021), while MRD− duration >24 months provided even better benefits in PFS (HR, 0.07, 95% CI, 0.03–0.19, p < .0001) and OS (HR, 0.1, 95% CI, 0.03–0.33, p = .0002). Comparison of PFS (Figure S2B) and OS (Figure 1B) among patients with MRD− duration >24 months, 12–24 months, and < 12 months indicated that longer MRD− sustainment was closely associated with better outcomes. One-month increase in the MRD− duration led to a reduction of 12.5% (95% CI, 0.841 ~ 0.911; p < .001) or 10.4% (95% CI, 0.854 ~ 0.941, p < .001) in the risk of progression/death or death, respectively. Multivariate analysis revealed MRD− duration ≥12 months as an independent factor for PFS and OS (Tables S2–S4; p < .001 for each). In contrast, although patients with MRD− < 12 months had longer PFS than those with MRD+ (Figure S2C; p = .0489), there was no significant difference in OS between them (Figure S2D; p = .1633). Together, these findings argue that the durability of MRD− is essential for its favorable prognostic impact. Emerging evidence supports a notion that MRD− may be better to predict patient outcomes than CR.6 We thus examined the temporal relationship between MRD− attainment and objective responses. In MRD− patients with ≥CR, 56.4% achieved MRD− at ≥CR, while in those with VGPR, 21.5% achieved MRD− at VGPR. In patients who achieved ≥CR as the best response, those with MRD− had significantly longer PFS (p < .0001; Figure S2E) and OS (p < .0001; Figure 1C) than their counterparts with MRD+. MRD− even more benefited patients who achieved VGPR as the best response (Figures S2F and 1D). Together, these observations support that the MRD status might predict patient outcome more precisely than conventional responses. To examine whether the MRD status would affect the prognostic properties of the baseline risk factors defined by the IMWG,4 we also examined the impact of the MRD status on the outcomes of patients with different CAs and ISS or R-ISS stages. Patients with HRCAs who achieved MRD− had significantly prolonged PFS (HR, 0.39; 95% CI, 0.30 ~ 0.52; p < .0001; Figure S3A) and OS (HR, 0.42; 95% CI, 0.30 ~ 0.59; p < .0001; Figure 1E) than their counterparts with MRD+. Similar phenomena were observed in patients with ISS III (Figure S3B; PFS: HR, 0.38; 95% CI, 0.29 ~ 0.51, p < .0001; Figure S3C; OS: HR, 0.45 95% CI, 0.32 ~ 0.64; p < .0001) or R-ISS III (Figure S3D; PFS: HR, 0.43; 95% CI, 0.29 ~ 0.66; p < .0001; Figure 1F; OS: HR, 0.54; 95% CI, 0.34 ~ 0.85; p = .0079). In patients with MRD−, there were no significant differences in both PFS and OS between patients with HRCA versus SRCA, ISS III versus I/II, or R-ISS III versus R-ISS I/II (p > 0.05 for each case). Notably, patients with HRCAs, ISS III, or R-ISS III who achieved MRD− even had better outcomes (particularly PFS) than those with MRD+ with SRCAs (PFS: HR, 0.31; 95% CI, 0.16–0.63, p = .0010; OS: HR, 0.48; 95% CI, 0.19–1.26, p = .1379), ISS I/II (PFS: HR, 0.30; 95% CI, 0.18–0.52, p < .0001; OS: HR, 0.44; 95% CI, 0.22–0.88, p = .0208), or R-ISS I/II (PFS: HR, 0.35; 95% CI, 0.17–0.71, p = .0035: OS: HR, 0.63; 95% CI, 0.27–1.49, p = .2938). In addition, patients with MRD− who received maintenance treatment had a trend for longer PFS and OS than those without maintenance but the differences were not significant (Figure S3E,F; p > .05 for both), likely due to limited sample size of the subgroups and follow-up time. Together, these observations suggest that attainment of MRD− might overcome the adverse prognostic impact of the risk factors at diagnosis, therefore support the notion that MRD status could re-stratify the risk of patients with HRCAs and advanced diseases (e.g., ISS III or R-ISS III). The main limitations of this study include that the MRD tests were not performed at fixed time points due to the retrospective nature, and that the limited sample size of subgroups did not allow detection of the impact of autologous stem cell transplantation (ASCT), and maintenance on the duration of MRD− and its related outcomes. Nonetheless, although our observations need to be further validated in appropriately pre-designed prospective studies, they might help address some concerns for the use of MRD assessment in daily practice and design future clinical trials involving MRD, eventually leading to tailored treatment according to the MRD kinetics. We thank all participating clinicians and patients for their support to this study. This work was supported by the National Natural Science Foundation of China (grant no. 81471165, 81670190, 81670189, 81870160, 81971108, and 82270207) , Science and Technology Development Program of the Jilin Province (grant no. 20190201042JC, 20190201163JC, and 20210509010RQ), and Interdisciplinary Integration and Innovation Project of JLU. The authors declared no potential conflicts of interest. Appendix S1. Supporting Information Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.